Heretofore, image forming methods using developers or toners to develop electrostatic latent images formed on an electrostatic latent image carrying member, e.g., a photosensitive member, and transferring said developer or toner image onto a recording member, e.g., a recording sheet, have been widely used in copiers, printers, facsimile machines and the like. More recently, full color image forming apparatuses, which reproduce multi-color images by overlaying a plurality of color developers or toners, have also become widely used. For example, in such full color image forming apparatuses, multi-color images are reproduced by forming an electrostatic latent image on a negatively charged organic photosensitive member by digital writing thereon via laser beam exposure or the like, reverse developing said electrostatic latent image using negatively chargeable magenta toner, cyan toner, yellow toner, and, as necessary, black toner, and then overlaying the developer/toner images of each said color to form a multi-color image.
To reproduce a multi-color image by overlaying the toner of each color, full color toners must have excellent transfer characteristics. When the amount of toner charge is too high, the adhesion force of the toner on the photosensitive member increases so as to reduce transfer characteristics even when the toner charge amount distribution is relatively broad. Accordingly, full color toners must possess a suitable amount of charge and charge amount distribution.
Designing full color image forming apparatuses for greater compactness has been studied in recent years, but such designs require greater compactness of the developing devices. This requirement is due to the fact that such full color image forming apparatuses require four developing devices to accommodate cyan developer, magenta developer, yellow developer, and black developer, respectively. In designing a developing device for greater compactness, it is beneficial to use nonmagnetic monocomponent developing devices that do not require a mixing mechanism to mix toner and carrier. In nonmagnetic monocomponent developing devices that do not use a carrier, the toner is charged via contact between a developer carrying member and a developer regulating member, such that this type of toner must characteristically be capable of rapidly attaining a suitable amount of charge. Furthermore, the toner must possess a hardness to prevent the loss of microparticles from the toner during contact between the developer carrying member and developer regulating member, as well as to prevent adhesion of the toner on the developer carrying member and developer regulating member.
Accordingly there remains a need for better and more reliable nonmagnetic monocomponent negatively chargeable color developers or toners, and methods for making same, that address the above problems and disadvantages and that provide a developer or toner having, for example, advantageous transfer, stability, charge rise and durability characteristics.